1. Field of the Invention
The present invention generally relates to a method for producing reflectors in continuous lengths of optical fiber. More particularly, the present invention involves the fabrication of reflectors in optical fibers by fusion splicing. The present invention also relates to apparatus which make use of fiber reflectors produced as a result of the claimed invention.
2. Description of the Prior Art
A number of methods for fabricating taps in optical fibers have been disclosed in the art. One such method involves the bending of the optical fiber axis in order to couple out some of the light which would ordinarily propagate through the substantially linear fiber. This method is used, for example, in the Siecor Model M67-210 Local Injection Detection System, as a means of monitoring the transmitted power in a fusion splicing unit. The tap produced as a result of this method of removing light is normally referred to as a macrobend tap.
A second method known in the art discloses the use of two fibers having relatively thin cores which are merged or placed in close proximity to each other so that at least some of the propagated light couples from one fiber to another. Such a method is generally disclosed in such commercial applications as the Amphenol Model 945 Fiber Coupler, often referred to as a fiber optic directional coupler.
Yet a third prior art method discloses the use of a reflective film deposited or evaporated on the ends of oblique optical fibers which are then physically combined at a joint or other similar bonding structure. In such prior art applications, a dielectric film, such as TiO.sub.2 or SiO.sub.2, is alternatively evaporated on the fiber ends in order to reflect part of the light propagated through the fiber. Couplers of this type generally utilize optical fibers cut at an angle of 45.degree. to their respective axis, and utilize optical cement for joining the fiber ends.
These prior art methods, however, suffer from a number of disadvantages. When light is coupled out by bending or distorting the linear axis of the optical fiber, it oftentimes becomes difficult to concentrate the propagated light into a small area photodetector. This disadvantage hinders high speed operation desirous in contemporary signal processing applications. Further, such a method couples light out in only a forward or lateral direction, but not in the reverse direction, as is often required in preferred applications.
Another significant disadvantage of prior art methods based upon macrobend or directional coupler taps is their tendency to introduce "modal noise" into the coupled fiber system. Recognizable as a spurious amplitude modulation at the receiver, modal noise is caused by the highly mode selective nature of the optical taps normally created between spliced fiber ends.
Other disadvantages of prior art methods include the general lack of structural integrity associated with the cementing of optical fibers coated with dielectric films. For practical applications for this kind of coupler, therefore, mechanical support is generally needed, which support greatly increases the overall bulk and expense of the final system.